Question 712133
Ignoring the alternating signs for the moment, for the sequence
 
{{{5}}}, {{{8}}}, {{{13}}}, {{{20}}}, {{{29}}}, ...
 
the nth term is given by {{{x = n^2 + 4}}}
 
We account for the alternating signs by multiplying each term by {{{-1^n}}} 
 
so the formula for the nth term in the original sequence is 
 
{{{x = (-1)^n * (n^2 + 4) }}}
 
and the next two terms are 40 and -53.